Skip to main content
Part of complete coverage on

New satellite data reveals sea-level rise

The city of Venice is investing billions in a new flood defence system to protect against sea level rises
The city of Venice is investing billions in a new flood defence system to protect against sea level rises
  • Global sea-levels rose by an average of 3 mm a year over the past two decades
  • Most accurate data yet based on satellite data from European Space Agency
  • Sea-level rises uneven around the world with Pacific region hit worst
  • Venice one of many cities upgrading flood protection barriers

Read a version of this story in Arabic.

(CNN) -- Sea-levels are rising unevenly around the world, with Pacific countries in particular suffering significant increases over the past two decades, according to accurate new satellite data.

On average, global sea-levels have been rising at about three millimeters (mm) a year, however, this masks large differences between regions of the world.

While some regions have seen sea-level rises of 12 mm a year, others have actually seen decreases of about 12 mm a year.

The results are based on radar readings from the European Space Agency (ESA) over an 18-year period from October 1992 to March 2010.

ESA used its satellites to send radar pulses to the sea surface below, recording the time delay in its return and creating a precise measurement of their height above the surface.

Special report: Sea-level rises

Scientists say sea-level rises are the result of the expansion of water due to rising temperatures, melting of glaciers and the melting of polar ice sheets.

Annual mean global sea-level changes 1992-2010 (ESA)  Annual mean global sea-level changes 1992-2010 (ESA)
Annual mean global sea-level changes 1992-2010 (ESA)Annual mean global sea-level changes 1992-2010 (ESA)

The worst hit regions over the past two decades, according to the ESA data, have been the Pacific countries of Indonesia, Papua New Guinea, Philippines and vulnerable Pacific islands like the Solomon Islands.

The Philippines for one is already frequently subjected to flooding and landslides caused by heavy rain, with seasonal monsoon rains in August killing at least 11 people.

Scientists suggest regions that have seen high sea level rises over the past 20 years will not necessarily continue to see higher than average sea-level rises in the future.

"We suspect that the bigger the differences get, the more they will tend to level out in the future," says Robert Meisner, a spokesperson for ESA.

However, a recent study of coastal cities still predicted the Philippines' capital Manila would see its vulnerability to flooding double by the end of the century, due to sea-level rises.

In some regions of the world, the increasingly accurate sea level data is being used by planners to mitigate against the risk of flooding.

See also: Five cities battling flooding, heats and storms

In Venice, where the sea-level data was released, engineers are constructing a new set of tidal barriers to protect the historic city.

The city, which attracts millions of tourists every year, is seeing sea-level rises of around 2 mm per year, together with slow, mostly natural, subsidence of about another 2 mm every year.

The new $7.9 billion-barrier system will see giant barriers placed on the sea floor around Venice. When the water levels rise, air will be pumped into the barriers raising them up to block the tidal flow and protect the city from flooding.

The system is due to be completed in 2014 and is expected to be able to protect the city for the next 20 years.

Part of complete coverage on
January 21, 2013 -- Updated 0230 GMT (1030 HKT)
Patricia Wu looks at efforts to combat food waste in Hong Kong.
January 14, 2013 -- Updated 0233 GMT (1033 HKT)
CNN's Pauline Chiou goes to Hong Kong's annual toy fair to find out about the growing market for eco-friendly toys.
December 31, 2012 -- Updated 0415 GMT (1215 HKT)
CNN's Liz Neisloss reports on a roof that is only a sample of the greening of Singapore's skyline.
December 19, 2012 -- Updated 0216 GMT (1016 HKT)
A dam project in Cambodia could destroy livelihoods and ecosystems, says Conservation International
December 18, 2012 -- Updated 0322 GMT (1122 HKT)
Shipping lines, port authorities and technology companies are taking the initiative to go green and reduce costs.
December 10, 2012 -- Updated 0206 GMT (1006 HKT)
Less than 20 miles from Singapore's skyscrapers is a completely different set of high-rise towers.
December 6, 2012 -- Updated 1104 GMT (1904 HKT)
The Pitcairn Islands might only have 55 human inhabitants, but the waters surrounding them are teeming with marine life.
December 3, 2012 -- Updated 0322 GMT (1122 HKT)
Biofuel made from sugar cane waste in Brazil could revolutionize the global energy industry.
November 26, 2012 -- Updated 0258 GMT (1058 HKT)
Many believe that fuel-cell cars will overtake electric vehicles in the near future.
November 19, 2012 -- Updated 0820 GMT (1620 HKT)
Modern and sustainable buildings in the UAE are taking cues from an ancient Arabic design tradition.
November 12, 2012 -- Updated 0409 GMT (1209 HKT)
One man's artistic vision is distracting divers from Cancun's threatened underwater ecosystem.
November 12, 2012 -- Updated 1746 GMT (0146 HKT)
Lake Victoria, Africa's largest lake, has been plagued by water hyacinth plants for over two decades.
A turtle on Australia's Great Barrier Reef
Just how much are natural wonders like the Great Barrier Reef worth in monetary terms?